Identification of exciton complexes in a charge-tuneable Janus WSeS monolayer

TL;DR

This study identifies specific exciton complexes in a charge-tuneable Janus WSeS monolayer with narrow linewidths, revealing their optical properties and potential for nanoscale sensing and energy harvesting applications.

Contribution

It is the first to precisely identify exciton transitions in Janus WSeS monolayers with narrow linewidths using advanced synthesis and heterostructure integration.

Findings

Identified neutral and charged exciton transitions with ~6 meV linewidth.

Confirmed direct bandgap at K points via magneto-optic measurements.

Demonstrated potential for applications in sensing and photovoltaics.

Abstract

Janus transition-metal dichalcogenide monolayers are fully artificial materials, where one plane of chalcogen atoms is replaced by chalcogen atoms of a different type. Theory predicts an in-built out-of-plane electric field, giving rise to long-lived, dipolar excitons, while preserving direct-bandgap optical transitions in a uniform potential landscape. Previous Janus studies had broad photoluminescence (>15 meV) spectra obfuscating their excitonic origin. Here, we identify the neutral, and negatively charged inter- and intravalley exciton transitions in Janus WSeS monolayer with $\sim 6$ meV optical linewidth. We combine a recently developed synthesis technique, with the integration of Janus monolayers into vertical heterostructures, allowing doping control. Further, magneto-optic measurements indicate that monolayer WSeS has a direct bandgap at the K points. This work provides the foundation for applications such as nanoscale sensing, which relies on resolving excitonic energy shifts, and photo-voltaic energy harvesting, which requires efficient creation of long-lived excitons and integration into vertical heterostructures.